Plant sap

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File:Stem-cross-section2.jpg
Multiple cross sections of a flowering plant stem showing primary and secondary xylem cells and phloem sieve tubes[1]

Plant sap, or just sap, is fluid transported in xylem tubes or phloem cells of a plant. Xylem cells transport water and inorganic nutrients through the plant; phloem cells transport sugarary fluids and other biological molecules.

Latex or resin is not plant sap. They are separately produced, with different components and functions.[2]

Types of plant sap[change | change source]

Xylem sap[change | change source]

Xylem sap is mainly water, with plant hormones, mineral elements and other nutrients in a dilute solution. Sap in xylem moves from roots towards the leaves.[3]

Phloem sap[change | change source]

Leafhoppers feeding on plant sap, attended by ants

Phloem sap is water, with manufactured sugars, other biological molecules and mineral elements dissolved in it. It flows from where carbohydrates are produced or stored to where they are used.[2]

A large number of animals, all of the single insect order Hemiptera, feed directly on phloem sap, and make it the primary component of their diet. Phloem sap is "nutrient-rich compared with many other plant products and generally lacking in toxins and feeding deterrents, [but] it is consumed as the sole diet by a very restricted range of animals".[4] Phloem sap is physiologically extreme in terms of animal digestion: it is thought that few animals take direct advantage of this because they lack adaptations to this diet.[4]

Many more consume phloem sap by proxy, feeding on the honeydew secretion] of phloem-feeding hemipterans. Honeydew is physiologically less extreme than phloem sap.[4] Others feed on the biomass of insects which have grown on direct ingestion of phloem sap.

Many products are made from plant sap. One of them is maple syrup. Maple syrup is made using sap from sugar maple trees.

Sap colour is different for different plants. e.g.:

  • Banana - colorless
  • members of Myristicaceae - sap red
  • members of Anacardaceae - black sap
  • members of gluciaceae - Yellow sap
  • Symphonia globilifera - Green sap

References[change | change source]